The present invention relates to an optical head which is used for an optical disk which allows erasure of information and which can emit a light beam for recording, reproducing or erasing the information with respect to the optical disk.
An optical disk is recently proposed which allows erasure of information and which has an erasable recording layer of a thermoplastic material, a material which changes its optical characteristics by a photomagnetic effect, or an amorphous alloy which changes its crystalline state to amorphous state upon being exposed to optical energy. In such an optical disk, for example, in an optical disk having an erasable recording layer of an amorphous alloy, the recording layer is heated rapidly and is rapidly cooled by a first laser beam to form an amorphous region in the recording layer to record information. The recording layer is gradually heated and is gradually cooled by a second laser beam to return the amorphous region of the recording layer into a crystalline state, thereby erasing information.
An optical disk used for an optical head having an erasable recording layer which allows erasure of information must be able to generate an erasing laser beam and a recording/reproducing laser beam from the viewpoint of characteristics of the recording layer. In view of this requirement, a conventional optical head has an optical system which has an erasing laser unit for emitting an erasing laser beam and a recording/reproducing laser unit for emitting a recording/reproducing laser beam and which can guide either the erasing laser beam or recording/reproducing laser beam to the recording layer. However, in the conventional optical head, since the optical system must be designed in view of the first and second laser beams, the optical system becomes complex, and the overall system becomes large and expensive.